Polyether polyols can be produced from polyhydroxyl compounds that are normally solid at ambient conditions, such as sucrose. One commonly used process for producing such polyether polyols is known as the “water process” in which the sucrose is dissolved in water prior to reaction with the selected alkylene oxide(s). The presence of sufficient water to completely dissolve the sucrose has been thought to be necessary since sucrose is non-reactive unless it is in a liquid phase. In addition, due to the presence of sufficient water to dissolve the sucrose, and to get the desired polyol functionality and viscosity, other water soluble liquid organic compounds, such as alcohols and/or amines, such as glycols, i.e., propylene glycol, are also often employed.
The presence of such an amount of water during the reaction of the sucrose with the alkylene oxide, however, can be undesirable. For example, excess water can take up significant space in a batch reactor which might otherwise be used to produce larger batches of polyether polyol. In addition, the presence of water can result in formation of difunctional glycols that reduce the arithmetically calculated functionality of the polyether polyol produced. As a result, in the typical “water process”, a dewatering step, usually distillation, is employed after a portion of the alkylene oxide has been added. Such removal of water after adding and reacting a portion of the total alkylene oxide desired reduces the amount of glycols formed and allows for a larger batch size, but still consumes significant time and energy.
A typical “water process” of the prior art is illustrated by FIG. 1. According to this process, a liquid organic compound, such as propylene glycol, is charged to a batch reactor (step 10), along with water (step 15), sucrose (step 20), and an alkali metal hydroxide catalyst (step 25). The water is present in an amount sufficient to dissolve the sucrose at the temperature at which the alkoxylation is to commence. After bringing the reactor to the desired alkoxylation temperature and pressure, a first portion of the alkylene oxide is fed to the reactor (step 30) at a selected feed rate or series of feed rates to conduct a first portion of the alkoxylation reaction. The reactor is then maintained at temperature for a period of time to allow the alkoxylation reaction to continue (step 35). Thereafter, water is removed from the reaction mixture (step 40), typically by distillation, until the water content of the reaction mixture is reduced to less than 10 percent by weight (normally significantly less than 10 weight percent). Then, a second portion of the alkylene oxide is fed to the reactor (step 45) at a selected feed rate or series of feed rates until all desired alkylene oxide has been fed. The reactor temperature may be maintained during this feeding of the second portion of alkylene oxide or it may be increased during the feed, if desired. The reactor is then maintained at temperature or increased in temperature for a period of time (step 50) to allow the alkoxylation reaction to proceed to completion. Thereafter, the resulting polyether polyol proceeds to catalyst neutralization and work-up (step 55).
It would be desirable to provide an improved “water process” for preparing highly functional polyether polyols in a batch process from polyhydroxyl compounds that are solid at ambient conditions, such as sucrose, wherein such a process does not employ a dewatering step prior to completion of the addition of the total alkylene oxide employed. Such a process should be simple and capable of producing a polyol of the same specifications as a similar polyol produced by prior art “water processes”. Such a process should also not negatively impact batch size and should not require the use of other materials, such as active hydrogen containing liquid organic compounds, such as glycols, and/or other materials not typically used in a “water process”, which may cause greater cost and/or complexity, for example.
The present invention has been made in view of the foregoing desire.